1. Field of the Invention
This invention relates to a polishing method for use in chemically and mechanically polishing and flattening the surface of a substrate such as a wafer having dielectric material layers or the like laminated, in a manufacturing process for a semiconductor device, and a polishing apparatus using the same, and is suitable, for example, in the lithography step of accurately detecting the polishing terminating point of the polishing step for an insulating film layer (film layer) applied to a silicon substrate and efficiently setting the film thickness of the insulating film layer to a predetermined range to thereby obtain a highly integrated semiconductor device.
2. Related Background Art
In recent years, with the tendency of semiconductor devices toward higher integration, the tendency of circuit patterns toward minuteness and the tendency of the device structure toward three dimensions have been advancing. If the numerical aperture of a projection optical system is made great to achieve the higher integration of the semiconductor device, the depth of focus of the projection optical system correspondingly becomes shallow. Therefore, it is important to polish the surface of the semiconductor device to thereby remove any level-difference portion and any uneven portion and flatten the surface, and apply photoresist onto the flattened surface, and projection-expose it to thereby achieve high resolution.
Also, it is an important factor for making the irregularity of the inter-layer capacity and the depth of via-holes constant to polish an insulating film layer provided on a silicon substrate to thereby provide a film layer of a uniform thickness.
A chemical-mechanical polishing method has heretofore been proposed as a flattening technique for removing the level difference portion and uneven portion of the surface of a semiconductor device to thereby flatten the surface.
In the chemical-mechanical polishing, it is necessary to appropriately control the polishing rate, the slurry density in polishing liquid and the temperature of a polishing surface in and to make the polishing efficient. If this control is defective, the insulating film provided on the silicon substrate will not assume a predetermined film thickness and the surface cannot be flattened and the aforementioned depth of focus cannot be secured and a reduction in the reliability of wiring will be caused, and also, the phenomena known as dishing and thinning due to the difference in polishing speed between the insulating film and an electrode wiring portion will occur to thereby cause short-circuiting or the like between via-holes.
Therefore, when the surface of a substrate such as a wafer having dielectric material layers or the like laminated is to be polished and flattened, it becomes important to appropriately judge the polishing terminating point and flatten the surface without removing the material of the lower layer.
For example, a terminating point detecting method of monitoring on the spot the film thickness of the surface of a substrate such as a wafer having dielectric material layers or the like laminated which is the object of polishing, and yet grasping the level of the flattening of the whole or localized part of the surface of the substrate such as the wafer and judging the optimum portion for terminating the polishing, becomes important in the chemical-mechanical polishing.
As the method of detecting the polishing terminating point, use has heretofore been made, for example, of a method of deducing the amount of polishing from the polishing time or a method of obtaining any change in polishing resistance from a change in the electric current of a polishing stool driving motor.
The method of obtaining the amount of polishing from the polishing time as a method of detecting the terminating point of polishing in the flattening of the surface of a semiconductor device by chemical-mechanical polishing requires to control conditions such as the pressing force of the semiconductor device, the degree of wear of a polishing pad, the density of slurry in polishing liquid and the temperature of a polishing surface constantly and therefore, it is difficult to detect the terminating point accurately.
Also, the method of obtaining any change in polishing resistance from a change in the electric current of a polishing stool driving motor requires to separate a signal waveform and noise from each other highly accurately and therefore, it is difficult to detect the terminating point accurately.
The present invention has as its first object the provision of a polishing method suitable, when chemically-mechanically polishing and flattening the surface of a substrate such as a wafer having dielectric material layers or the like laminated, for utilizing an appropriately designed film thickness measuring method or/and film thickness measuring means to thereby directly monitor the film thickness of the surface on the spot and measure the film thickness distribution on the whole or localized part of the surface, and optimize the polishing conditions from the measured information and efficiently flatten the surface of a semiconductor device, and enhance the detection accuracy of a polishing terminating point and manufacture a semiconductor device having a high degree of integration, and a polishing apparatus using the same.
Other objects of the present invention will become apparent from the following detailed description of the preferred embodiments of the invention.